ATX
I'd say ATX was the most popular form factor. Assuming microATX and the like is included in that. BTX also existed at that time however, it never really caught on
Most popular
No Dannii minogue is,Danni was voted the most popular judge on the x factor in 2009.
The most popular
tulisa
"What Makes You Beautiful" is probably the most popular.
Rebeca or mat
Kelly rowland
ATX (most commonly used today), BTX, LPX, NLX, backplane systems, and the outdated ATform factorpages 143-150 of A+ Guide to Managing & Maintaining Your PC, Sixth Edition by Jean Andrews
The most popular would be Jeep or Jeepney.
The most popular form of tax at the county level is sales tax.